1. Field of the Invention
The present invention relates to a sulfonic acid polyol compound, a polyurethane resin, a polyurethane resin for a magnetic recording medium, and a magnetic recording medium.
2. Description of the Related Art
Sulfonic acid compounds are generally highly water-soluble but organic solvent-insoluble compounds, and the use thereof as synthetic organic chemicals is limited. For example, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (CAS No: 10191-18-1) is a sulfonic acid compound that has two hydroxy groups but does not dissolve in organic solvents, and the application thereof is therefore limited to reactions in a heterogeneous system or reactions in an aqueous system.
Furthermore, JP-A-3-66660 (JP-A denotes a Japanese unexamined patent application publication) discloses a method for producing an N,N-bis(hydroxyethyl)aminoethylsulfonic acid salt, etc.
Magnetic recording technology has the excellent features, not seen in other recording methods, that the medium can be used repeatedly, signals are easily converted to electronic form and it is possible to build a system in combination with peripheral equipment, and signals can easily be corrected, and is therefore widely used in various fields including video, audio, and computer applications.
In general, with the demand for higher recording density in magnetic recording media for computer use, etc., it is necessary to yet further improve the electromagnetic conversion characteristics, and it is important to make a ferromagnetic powder finer, the surface of the medium ultra smooth, etc.
With regard to making a magnetic substance finer, a ferromagnetic metal powder of no greater than 0.1 μm or a ferromagnetic hexagonal ferrite fine powder having a plate size of no greater than 40 nm has recently been used as a magnetic substance. In the case of a multilayer structure in which a magnetic layer is provided as an upper layer after a non-magnetic lower layer is provided on the surface of a support, in order to highly disperse in a binder a fine non-magnetic powder used for the non-magnetic layer or the fine magnetic substance above, a dispersion technique has been proposed in which a hydroxy group or the hydrophilic polar group —SO3M (M denotes hydrogen, an alkali metal, or an ammonium salt) is introduced into the binder, and a binder chain is made to adsorb on the magnetic substance or the non-magnetic powder via the polar group so as to achieve a smooth surface.
For example, JP-A-9-138939 discloses a magnetic recording medium in which a magnetic material having a ferromagnetic powder dispersed in a binder is applied onto a non-magnetic support, wherein the magnetic layer comprises as a binder component a polyurethane resin formed from a high molecular weight polyol having a molecular weight of at least 500 (A), an organic diisocyanate (B), and as necessary a polyol compound having a molecular weight of no greater than 500 (C), the high molecular weight polyol (A) comprising a hydrophilic polar group-containing aromatic polyester diol (A-1) whose dibasic acid component is an aromatic dibasic acid, and another high molecular weight polyol (A-2).
Furthermore, JP-A-5-70545 discloses a polyether polyurethane resin in which a polyol molecule component and a polyether molecule component are chain-extended via a urethane bond, the resin having a weight-average molecular weight of 20,000 to 200,000 and the polyether component being a polyether polyol employing as an initiator a low molecular weight diol having an SO3M group (M is an alkali metal atom or a hydrogen atom), a binder for a magnetic recording medium comprising the polyurethane resin, and a magnetic recording medium.